This document is intended to provide notes on the origin, format,
limitations etc of all ROSAT calibration datasets within the
http://legacy.gsfc.nasa.gov/docs/heasarc/caldb/caldb_intro.html
By its nature, it is therefore very much a 'live' document and
is expected to expand rapidly throughout the operational phases of the
mission.

In the rest of this chapter, the location and structure of the
http://legacy.gsfc.nasa.gov/docs/heasarc/caldb/caldb_intro.html
at
http://www.gsfc.nasa.gov
at is briefly described, along with references
to other relevant documentation.
All ROSAT XRT, PSPC & HRI datasets within the caldb at NASA/GSFC
are then summarized in Chapters 2,
3 &
4
respectfully, with non-instrument specific datasets summarized in
Chapter 5.

The location, organization and contents of the
http://legacy.gsfc.nasa.gov/docs/heasarc/caldb/caldb_intro.html
on-line at
http://www.gsfc.nasa.gov
is summarized in OGIP Calibration Memo CAL/GEN/93-006
(available on-line as
ftp://legacy.gsfc.nasa.gov/caldb/docs/memos/cal_gen_93_006/cal_gen_93_006.ps
and
http://legacy.gsfc.nasa.gov/docs/heasarc/caldb/docs/memos/cal_gen_93_006/cal_gen_93_006.html
versions).

The contents of the /caldb area is sub-divided between
the following sub-directory trees:

data
- containing the calibration dataset directory tree.

software
- containing the caltools software tasks, the
callib
subroutine library and a number of other software-related items.

docs
- containing related calibration documentation

Here we only consider the data tree.
It should be noted that access to certain caldb directory
trees is also available from other
areas of the legacy anonymous ftp account
via symbolic links (see CAL/GEN/93-006,
available on-line as
ftp://legacy.gsfc.nasa.gov/caldb/docs/memos/cal_gen_93_006/cal_gen_93_006.ps
and
http://legacy.gsfc.nasa.gov/docs/heasarc/caldb/docs/memos/cal_gen_93_006/cal_gen_93_006.html
versions).

The OGIP caldb classifies files as `Primary Calibration Files',
`Basic Calibration Files' and `Calibration Product Files'
(PCFs, BCFs & CPFs respectively; see also CAL/GEN/91-001,
available on-line as
ftp://legacy.gsfc.nasa.gov/caldb/docs/memos/cal_gen_91_001/cal_gen_91_001.ps
and
http://legacy.gsfc.nasa.gov/docs/heasarc/caldb/docs/memos/cal_gen_91_001/cal_gen_91_001.html
versions).
PCFs are 'raw' ground and in-orbit calibration datasets not of
immediate interest to most users as they are not directly required for
(all but the most specialized) scientific data analysis tasks.
These dataset are not considered here.
BCFs contain the lowest level calibration datasets potentially required
by downstrem software, and can be considered the `atomic units' of the
instrument calibration.
CPFs contain `convolutions' of the information stored within BCFs
customized for a specific analysis task and/or scientific observation.

All BCF & CPF calibration files are organized using the scheme

/caldb/data/mission/inst

where mission & inst are the OGIP-standard names
for the mission and instrument.
For internal management purposes, a further division into
inst/bcf and inst/cpf sub-directories is
made in most cases.
Non-instrument specific calibration datasets, including general spacecraft
housekeeping information etc,
can be found in the
/caldb/data/mission/mis sub-directory.

Throughout this document, the hash (#) symbol is used as a wild-card
in filenames to indicate several files are available with slightly
different names. In all cases the detailed naming scheme, along with the
characters which can be used to replace the # are described in the
detailed description of the file set.

PLEASE NOTE:
The filenames and locations of the calibration datasets described within this
document were chosen by the
http://legacy.gsfc.nasa.gov/docs/rosat/rosgof.html
in collaboration with the instrument teams. Please dont complain to
the CALDB if you consider them confusing, inappropriate etc.

The information within this document obviously could not have been compiled
without the help of very many people within the ROSAT XRT, PSPC &
HRI instrument teams, to whom we owe an enormous debt.
Wherever possible we acknowledge the direct source of the information
within the text, but undoubtedly this may often under-represent the
collective effort involved.
We apologise to anybody who has inadvertently not been credited,
and will be happy to add their name in the appropriate place(s).

These two datasets, using a naming scheme
xrt_vi.eff_area (where i=1 & 2), contain the
effective areas of the XRT (including vignetting) as a function of energy
(729 bins) and off-axis angle (14 values).

These datasets were converted to OGIP FITS format
from the ASCII files area_b_1.asc &
area_b_2.asc (for i=1 & i=2 respectively)
supplied by Steve Snowden (ROSAT GOF, NASA/GSFC).
The area_b_*.asc files consist of the (total) spectral
response for PSPCB. The current dataset was therefore created
by DIVIDING the corresponding area_b_*.asc dataset by:

the gas efficiency: pspc_v1.gas_eff

the window transmission: pspcb_v1.wind_trans

(The area_b_1.asc & area_b_2.asc
datasets have also been converted to
an OGIP FITS format as is stored in files
pspcb_v1.spec_resp & pspcb_v2.spec_resp)

Points to Note

The XRT effective area is assumed to be independent of azimuthal
angle.

The dataset xrt_v1.eff_area
was only used for a short period early in the
mission, until it was superceded by
xrt_v2.eff_area.

The area_b_2.asc dataset from which this dataset is derived
appears to be identical to that known as SASS_AREA_B_NEW2.FITS
by the SASS processing software (and distributed on US (Rev0)
GO tapes
within the rp*****.oar file)

This dataset consists of the vignetting function (in the range
0.0 ® 1.0) of the XRT as a function of energy
(729 bins) and off-axis angle (14 values).
The geometric reduction in collecting area at high off-axis angles
is included.

This dataset was converted to OGIP FITS format
from the ASCII file
area_b_2.asc
supplied by Steve Snowden (ROSAT GOF, NASA/GSFC).
The area_b_2.asc file consist of the (total) spectral
response for PSPCB. The current dataset was therefore created
by DIVIDING the area_b_2.asc dataset by:

the gas efficiency: pspc_v1.gas_eff

the window transmission: pspcb_v1.wind_trans

the on-axis effective area (stroed within area_b_2.asc)

(The area_b_2.asc
dataset has also been converted to
an OGIP FITS format as is stored in file
pspcb_v2.spec_resp)

Points to Note

The vignetting is assumed to be independent of azimuthal
angle.

The area_b_2.asc dataset from which this dataset is derived
appears to be identical to that known as SASS_AREA_B_NEW2.FITS
by the SASS processing software (and distributed on US (Rev0)
GO tapes within the rp*****.oar file)

The dataset is used to correct for non-linearities in the width of
the PHA channels introduced by the PSPC analogue-to-digital converter.
The effective lower & upper boundaries of each channel (PH_1)
are stored in columns ADC_LO & ADC_HI respectively.
These values
were derived by MPE by fitting a smooth spline to a cumulative
spectrum of a large number of ground calibration measurements.
The dataset is assumed to be valid for both PSPCC & PSPCB

Given an event with an observed PH channel, a random-number generator
can be used to find the effective channel PH_1, corrected for the
ADC nonlinearities, by assuming equal probability between the
appropriate values of ADC_LO & ADC_HI. However, it
should be noted
that the effective channel so derived is NOT the Pulse-Invariant (PI)
channel for that event - further spatial & temporal gain corrections
have also to be applied.

Delivered to CALDB by:

Rehana Yusaf (ROSAT FTOOLS) 1995 Oct 06, after having been
was converted to FITS
from the ASCII file ADC_BINS.DAT used by SASS.

Two files, alkhist_v1_b.fits & alkhist_v1_c.fits
(for PSPCB & PSPCC respectively),
containing the
the results from measurements taken using the
on-board Aluminum calibration source when fitted with a Prescott
function. The peak channel (given in column ALK_BIN) in which the
Aluminum line falls therefore gives an estimation of the "Gain" of
the detector. Variations in gas density, composition, high voltage,
pressure and temperature give rise to variations in gain. Thus, this
can be used to correct for the gain of the detector at a given
observational epoch by linearly interpolating between the Aluminum
calibration measurements before and after the observation.

The times stored in the dataset (in column ISCC) are as measured
by the spacecraft clock, and apply to the END of the ROSAT-day
to which they refer. In cases when more than one Al measurement
were taken on a given ROSAT-day (as denoted when the value in
column N_PTS are greater than one), the values stored in the
ALK_BIN & ALK_FWHM cloumns are the means of the values
obtained from the individual fits.

No further information beyond that given above
(see also
http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/cal_ros_95_010_summary.html

Points to Note

1995 Oct 17 (Ian M George, HEASARC)

It should be noted that there are a number of other corrections
must be applied to correct for various other detector effects.
See
http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/cal_ros_95_010_summary.html
for for further details.

The file alkhist_v1_b.fits
is only valid for the PSPCB detector, which was used
after the destruction of PSPCC on 1991 Jan 25 (Spacecraft
clock time: 20606971.33 s). It should be noted that on 1991 Oct 11
(Spacecraft clock time: approx 42910000.0 s), the High Voltage of
the detector was intentially lowered from 3060 to 3000 V which
results in the gain (and hence peak channel of the Al measurements
to decrease by approximately 30%).

The file alkhist_v1_c.fits
is only valid for the PSPCC detector, which was used
during the PV and All-Sky-Survey phases of the mission until its
destruction on 1991 Jan 25 (Spacecraft clock time: 20606971.33 s)

Two files, gain_kor3_b.fits & gain_kor3_c.fits
(for PSPCB & PSPCC respectively),
required to
correct for small-scale non-linearities which
are introduced into the positions assigned to PSPC events by the
detector wires. This dataset contains the two position-dependent
correction vectors, stored in columns SGC_LF_Y &
SGC_HF_Y, both of
which vary as a function of position
(stored in column Y_1).

Delivered to CALDB by:

Rehana Yusaf (ROSAT FTOOLS) 1995 Oct 06, after having been
was converted to FITS from the ASCII files
GAIN_KOR3_B.DAT & GAIN_KOR3_C.DAT
used by SASS.

No further information beyond that given above
(see also
http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/cal_ros_95_010_summary.html

Points to Note

1995 Oct 17 (Ian M George, HEASARC)

It should be noted that a further vector, which is a function of
pulse height (only), is also required to correct the position of
each event for these electronic effects. Furthermore, an additional
correction due to the bulging of the detector window must be performed
on the position of each event before totally linearized detector
coordinates are obtained.

The dataset is used to correct for small-scale non-linearities which
are introduced into the positions assigned to PSPC events by the
detector wires. This dataset contains the energy-dependent
correction vector, stored as a function of intermediate pulse-height
(PH_3) in column SGC_HF_E.
This dataset is assumed to be valid for both PSPCs.

Delivered to CALDB by:

Rehana Yusaf (ROSAT FTOOLS) 1995 Oct 06, after having been
was converted to FITS from the ASCII file
GNAMPL_NEW.DAT
used by SASS.

No further information beyond that given above
(see also
http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/cal_ros_95_010_summary.html

Points to Note

1995 Oct 17 (Ian M George, HEASARC)

It should be noted that further vectors, which are a function of
position (only), are also required to correct the position of
each event for these electronic effects. Furthermore, an additional
correction due to the bulging of the detector window must be performed
on the position of each event before totally linearized detector
coordinates are obtained. Finally it should be noted that
PH_3 is
NEITHER observed PHA channel
NOR derived PI channel, but is instead
a partially corrected pulse-height bin.

The dataset is used when correcting the positions assigned to
PSPC events for slight offsets arising from the bulging of the
detector window as a result of the internal gas pressure versus
the external vacuum of space. The distortions introduced are a
function of both position and energy, however the dependencies
are assumed to be separable. This dataset is normalized to unity
at 0.93 keV (since the position-dependent corrections, sometimes
refered to as the Golden Disc) were determined from measurements at
that energy. The function is stored as a function of
Pulse-Invariant (PI) channel in column WC_GA_E.
This dataset is
is assumed to be valid for both PSPC detectors.

Delivered to CALDB by:

Rehana Yusaf (ROSAT FTOOLS) 1995 Oct 06, after having been
was converted to FITS from the ASCII file
SCAL3.DAT
used by SASS.

No further information beyond that given above
(see also
http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/cal_ros_95_010_summary.html

Points to Note

1995 Oct 17 (Ian M George, HEASARC)

It should be noted that further vectors, which are functions of
position (only), are also required to correct the position of
each event for the window distortion. Furthermore, an additional
correction due to electronic effects in the detector window must
be performed on the position of each event (first) before totally
linearized detector coordinates are obtained.

Two maps for each PSPC giving the position-dependent correction for
each event in the X- & Y-axes. The naming convention used is:
tabM_093_N.fits
where M is either x or y denoting the map contains the
correction for the X- or Y-axes respectively,
and N is either b or c denoting the map refers to
PSPCB or PSPCC respectively.

These maps are
used when correcting the positions assigned to
PSPC events for slight offsets arising from the bulging of the
detector window as a result of the internal gas pressure versus
the external vacuum of space. The distortions introduced are a
function of both position and energy, however the dependencies
are assumed to be separable.

The data were determined from ground calibration
measurements made at 0.93 keV. The dataset is stored as a
2-dimensional array as a function of X_1 &
Y_1, which are
detector coordinates of an event AFTER the electronic
correction has been applied.

No further information beyond that given above
(see also
http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/cal_ros_95_010_summary.html

Points to Note

1995 Oct 17 (Ian M George, HEASARC)

It should be noted that a further vector, which is a function of
energy (only), is also required to correct the position of
each event for the window distortion. Furthermore, the
correction due to electronic effects in the detector window must
be performed on the position of each event (first) before totally
linearized detector coordinates are obtained.

The data contained within these files are the mean PI channels of spectral
fits of the on-board Al K alpha calibrations. Typically, data were
collected from calibration intervals spanning about 100 days in order
to achieve reasonable statistics. The range of applicability of each
image is given by the range of ROSAT day number denoted in their
filenames (and obviously also by header keywords within the file).

Stepping in 2 arcmin intervals in both DETX and DETY, circular
regions were analyzed where the radius of the regions were set to provide
approx 2500 counts. This usually required radii between 3 and 6 arcmin so the
fits are not independent.

The fits were performed using the proportional counter response model of
Jahoda and McCammon fixing all parameters except the gain,
normalization, and a constant background. The mean channel for the
fit of all events can be found in pixel(1,1). It has a typical value
of slightly more than 152. The mean PI channel over the field can
vary between 145 and 158.

A total of 26 detector maps constructed by Snowden et al. in 13
channel ranges for each of the two PSPCs. The naming scheme is such that
file det_n_m_X.fits contains the map for PSPC-X over the channel
range n-m (out of the full resolution 256 channels).

These detector efficiency maps were created by using events from the
ROSAT all-sky survey in detector coordinates to approximate a flat field.
Point sources, particle contamination and times of short-term noncosmic
background enhancements were excluded from the data set. Furthermore, an
estimate of the residual particle background contribution to the data was
subtracted.

Creating the maps from such a pseudo flat field has an advantage over
using the theoretical vignetting function in that it accurately reflects
all detector and telescope nonuniformities. Specific examples of such
nonuniformities are the shadowing by the wires and ribs of the window
support structure, electronic "ghost" images in the R1L (and R1) band,
and variations in the window thickness and therefore the detector quantum
efficiency as a function of position. The maps depend on the X-ray spectrum
and their creation for each pulse-height band reflects the average spectrum
of the soft X-ray diffuse background. This will create no problems in the
lowest pulse-height bands where the vignetting is little changed over the
energy range covered by the band. However, for the highest pulse-height
band, if the spectrum of an extended object is much different from that of
the SXRB, the vignetting correction will lose accuracy.

Points to Note

Jane Turner (ROSAT GOF) 1995 Nov 17

The maps for the two PSPCs are not the same. Besides detector-specific
artifacts, there is a small shift in the position of the window support
structures and the windows have slightly different thickness distributions.
The main survey was done with the first PSPC ( ~ 180 days), and there were
~ 11 days of survey with the second PSPC to extend the sky coverage in
exposure gaps of the main survey. Because of this, data exist to create
maps for both detectors. However, the statistics of the second PSPC data
are obviously significantly worse than those of the main survey, and are
inadequate for determining the fine structure in the maps for bands R3
through R7. For these bands, templates were created by shifting the maps
of the first PSPC to correctly align the shadows of the window support
wires and ribs with the second PSPC. The shifted maps were then normalized
to the maps of the second PSPC over overlapping 5'x5' regions to give the
correct telescope vignetting and detector quantum efficiency.
Unfortunately, the systematics of the detector artifacts in the R1 and R2
bands are sufficiently different between the two detectors to preclude
using the same scheme for these bands. So, despite the worse statistics,
the maps for the second PSPC for these bands were created using only the 11
days of survey data taken with this detector.

The pixel size of the maps is 14.947" x 14.947". The reason for this
somewhat obscure pixel size is that the PSPC detector position digitization
is 0.934208"and the detector coordinates were binned by 16 for the maps.
Note that this is not an integral number of SASS event-position intervals
(0.5"), or the same pixel size as the SASS event images (15"x15").
The maps were normalized to the on-axis value by fitting the radial
distribution of the inner 18' radius region of the PSPC to the theoretical
vignetting function (Molendi 1993). The average shadowing by the window
support wires is therefore not included in the exposure correction;
however, it is included in the window transmission for modelling purposes.
The spatial structure of the shadowing caused by the window support wires
and the window support ribs is included in the exposure correction produced
by the maps.

The effects of electronic ghost images are very obvious in the
regularly spaced bright spots and somewhat less-bright lines. The PSPC is
an imaging proportional counter that makes use of induced charge on crossed
cathode wires to obtain the position of accepted events. The
two-dimensional position determination is done using the largest signals on
the crossed cathodes, essentially interpolating the event position between
the two nearest cathode wires in each direction. For very low pulse-height
events, there is the possibility that only one cathode in one or both
directions will have signals above the lower level discriminator of the
analog electronics chain. In this case, the position determination
degenerates to the center of the nearest cathode, yielding a line (if only
one axis has a single nonzero cathode value) or a point (if both axes have
only one nonzero cathode value each).

Also visible in the detector maps is a slight bending of the
electronic ghost-image lines. This detector artifact is due to the
position correction algorithm. The algorithm corrects the event position
based on the assumption that the X-ray was absorbed in the counter gas near
the window. The bulging of the window support structure by the pressure of
the counter gas bends the electric field lines in the electron drift region
of the PSPC. This causes a displacement of the event position, an effect
which has been calibrated and is included in the SASS event
position-correction procedure. Since the low pulse-height events which
contribute to the electronic ghost images have detected positions shifted
to the wire positions, this correction is not the appropriate one.

Electronic ghost images strongly affect only the R1 and R1L band maps,
although the R2 band map also shows some irregularities. However, since
the electronic ghost images are pulse height and not energy dependent, the
R1 map created from the high-gain data is reasonably appropriate for
correcting the R1L band data collected in the low-gain state (where no
survey data exist to produce a flat field). This works because the R1L
band at low gain includes the same pulse heights at its low end as the R1
band at high gain. The weighting by the source spectrum is of course
slightly different, but this is a small effect in this energy range. The
R1 maps should be used for R1 band analysis for data collected during
high-gain operation. The R1 map should also be used for R1L band analysis
for data collected during low-gain operation. We have created R1L maps for
both detectors to be used in R1L band analysis ONLY for data collected
during high-gain operation. (Note that the R1L band nomenclature refers to
the 11-19 channel band, which must be used for observations taken at low
gain. However, the R1L band can also be used for observations taken at high
gain. This is even preferable if an image derived from high-gain data will
be compared with an image derived from low-gain data. To make sense of all
this, remember that the PI channels are adjusted to always correspond to
the same energy, so the corresponding pulse height will change with gain.)

were produced using the calibration results of Plucinsky et al. (1993).
The naming scheme used is detp_n_x.fits,
where x is the gain state
of the detector (h or l), n is the component of particle
background where

i denotes the internally produced component,

e denotes an externally produced component, and

ap denotes the component made up
from low pulse-height events which follow a precursor event.

The 'ap' events are related to the total particle background rate.

The maps have 14.947" x 14.947" pixels (the 0.934208" x 0.934208" PSPC
detector pixels binned by 16 in both X and Y), the same scale as the
detector efficiency maps used for exposure correction and the casting of
other noncosmic backgrounds . We have generated three maps (one for the
first PSPC, two for the second PSPC for the two gain states) based on the
radial functions which were used to fit the FWC data. The high gain state
is denoted 'h', and is appropriate for data taken before Oct 11 1991, the
low gain state is denoted 'l', and is appropriate for data taken after
that date.

The following matrices are 2-dimensional arrays (energy vs channel)
containing the probabilities that a photon of a given incident energy which
enters the detector will give rise to an event in a given PI channel.
As such they are VALID FOR ALL REGIONS of the detector, but
also require
an appropriately constructed Äncillary Response File" (ARF) to enable
spectral analysis to be performed in XSPEC:

The pspc#_gain2#
matrices include a 'fudge' derived from
a 1992 observation of Mkn421 made primarily to correct a ~ 10%
systematic deficit
in photons versus model observed in a large number of sources. It should be
noted that these matrices have had a one channel (of the 256) downward shift
applied with respect to all previous matrices. This is equivalent to a
change in the zero-offest of the ADC (within the uncertainties given the
lack of ADC zero-offset measurement pre-launch) and represents a 5%
lowering of the gain. The necessity of such a change was determined from
the fits to several datasets, with the formal actual best-fit actually
being slightly less than a whole channel, but close enough (and uncertain
enough) for one channel to be used for simplicity.

Points to Note

The accuracy of the PSPC Spatial/Temporal Gain Calibration
used in the construction of this dataset is described
in OGIP Calibration Memo
http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/cal_ros_95_003_summary.html

The pspc#_gain2#
matrices include a 'fudge' derived from
a 1992 observation of Mkn421 made primarily to correct a ~ 10%
systematic deficit
in photons versus model observed in a large number of sources. It should be
noted that these matrices have had a one channel (of the 256) downward shift
applied with respect to all previous matrices. This is equivalent to a
change in the zero-offest of the ADC (within the uncertainties given the
lack of ADC zero-offset measurement pre-launch) and represents a 5%
lowering of the gain. The necessity of such a change was determined from
the fits to several datasets, with the formal actual best-fit actually
being slightly less than a whole channel, but close enough (and uncertain
enough) for one channel to be used for simplicity.

Points to Note

These datasets are valid on-axis ONLY

The accuracy of the PSPC Spatial/Temporal Gain Calibration
used in the construction of this dataset is described
in OGIP Calibration Memo
http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/cal_ros_95_003_summary.html

The following matrices are 2-dimensional arrays (energy vs 34 channel)
containing the probabilities that a photon of a given incident energy which
enters the detector will give rise to an event in a given PI channel.
The 34 channels are those used by SASS.
These matrices are VALID FOR ALL REGIONS of the detector, but
also require
an appropriately constructed Äncillary Response File" (ARF) to enable
spectral analysis to be performed in XSPEC:

These datasets use the 34 SASS channels (rather than the
full 256 channels provided by the PSPCs).

The accuracy of the PSPC Spatial/Temporal Gain Calibration
used in the construction of this dataset is described
in OGIP Calibration Memo
http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/cal_ros_95_003_summary.html

These datasets use the 34 SASS channels (rather than the
full 256 channels provided by the PSPCs).

The accuracy of the PSPC Spatial/Temporal Gain Calibration
used in the construction of this dataset is described
in OGIP Calibration Memo
http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/summary/cal_ros_95_003_summary.html

This dataset was created using bright-Earth data from the SASS files.
Data were
selected when the Count rate was greater than 8 counts/s and the zenith
angle was greater than 115 degrees. This detector map is for the
vignetted component of HRI data, i.e. it should be used to cast effective
exposure.

Delivered to CALDB by:

Steve Snowden (ROSAT GOF at NASA/GSFC) on 1995 Apr 20.

File Format

No formal multi-mission format (simple 2D image in Primary array)

Input Datasets, Assumptions, etc

As above

Points to Note

Map is for the vignetted component of HRI data, and
should be used to cast effective
exposure.

This dataset was created using dark-Earth data from the SASS files.
Data were selected
when the Count rate was greater than 8 counts/s and the zenith angle was
greater than 115 degrees. This detector map is for the unvignetted component
of HRI data, i.e., it should be used to cast the particle background. The raw
map was corrected for residual vignetted X-rays

Delivered to CALDB by:

Steve Snowden (ROSAT GOF at NASA/GSFC) on 1995 Apr 20.

File Format

No formal multi-mission format (simple 2D image in Primary array)

Input Datasets, Assumptions, etc

As above

Points to Note

Map is for the unvignetted component of HRI data,
and should be used to cast the particle background.